Thermal driven water desalination system using forward osmosis

Abstract

A system and method for water desalination using forward osmosis to address problems associated with scarcity of freshwater around the world. The system uses ammonium bicarbonate as the draw solution to draw out freshwater through a forward osmosis (FO) membrane from an amount of saltwater or other contaminated water initially directed through one side of the FO membrane. The ammonium bicarbonate draws the desalinated water through the membrane of the FO membrane. Brine or other solutes are directed away. The combination of desalinated water and ammonium bicarbonate is directed through a series of valves and pumps, including a heat pump, and through a hydrophobic membrane that allows freshwater (product water) to be obtained from the desalination process in a more cost-effective and efficient manner. The ammonium bicarbonate is recycled and reused to generate additional draw solution for additional batches of saltwater or contaminated water for desalination.

What is claimed is: 
     
       1. A water desalination method that uses forward osmosis, comprising:
 (a) creating a vacuum in a water desalination system; 
 (b) after creating the vacuum in the water desalination system, flowing salt water or contaminated water to be desalinated through a feed side of a forward osmosis (FO) membrane housing, wherein the salt water or the contaminated water to be desalinated is at ambient temperature; 
 (c) after step (b), while flowing the salt water or the contaminated water through an inlet of the feed side of the FO membrane housing, flowing a concentrated ammonium bicarbonate solution through an inlet of a draw side of the FO membrane housing, wherein the feed side and the draw side of the FO membrane housing are separated by a FO permeable membrane, 
 wherein the concentrated ammonium bicarbonate solution functions as a draw solution in the FO membrane housing, 
 wherein a temperature of the concentrated ammonium bicarbonate solution is also at ambient temperature; 
 (d) as a result of osmotic pressure, allowing a minimum period of time for the concentrated ammonium bicarbonate to pull a percentage of desalinated product water from the feed side through the FO permeable membrane to the draw side of the FO membrane housing; 
 (e) flowing brine or other extracted contaminant solutes pulled through the FO membrane housing in the feed side of the FO membrane housing to a collection point for the brine or the other extracted contaminant solutes, further comprising flowing the brine or the other extracted contaminant solutes to a first vacuum tank and pumping the brine or the other extracted contaminant solutes one or more time in and out of the first vacuum tank before redirecting the brine or the other extracted solutes to another location for further processing or collection; 
 (f) flowing a resulting solution through the draw side of the FO membrane housing from the draw side of the FO membrane housing, wherein the resulting solution is a combination of the percentage of the desalinated product water and the concentrated ammonium bicarbonate solution and wherein the resulting solution is a diluted ammonium bicarbonate solution; 
 (g) pumping the resulting solution to a water heat pump, wherein the water heat pump has a load side and a source side, wherein the load side is divided from the source side of the water heat pump; 
 (h) flowing the resulting solution through the load side of the water heat pump, further comprising, using the water heat pump to heat or raise a temperature of the resulting solution as the resulting solution is flowing through the load side of the water heat pump; 
 (i) after step (h), flowing the heated resulting solution to a feed side of a hydrophobic membrane housing, wherein the hydrophobic membrane housing comprises a hydrophobic membrane that permits gases to flow through the hydrophobic membrane from the feed side of the hydrophobic membrane housing to a draw side of the hydrophobic membrane housing, wherein the gases are ammonia, carbon dioxide, and water vapor; 
 (j) allowing the heated resulting solution to be filtered through the hydrophobic membrane of the hydrophobic membrane housing, wherein any ammonium bicarbonate ions in the heated resulting solution are converted or dissociate into the gases in the feed side of the hydrophobic membrane housing, wherein the gases pass through the hydrophobic membrane from the feed side of the hydrophobic membrane housing to the draw side of the hydrophobic membrane housing, leaving behind freshwater product water to flow out of the feed side of the hydrophobic membrane housing without ammonium bicarbonate ions present in the freshwater product water; 
 (k) flowing the freshwater product water from the feed side of the hydrophobic membrane through a first dividing valve; 
 (l) after passing through the first dividing valve, directing a first amount of the freshwater product into an inlet of the source side of the water heat pump and re-directing a second amount of the freshwater product water directly to a second vacuum tank; 
 (m) directing the freshwater product from the water heat pump to a second dividing valve further comprising dividing up the first amount of freshwater product that has been cooled into a first amount of cooled freshwater and a second amount of cooled freshwater; 
 (n) directing the first amount of the freshwater product to the second vacuum tank; and 
 (o) directing the second amount of cooled freshwater to the draw side of the hydrophobic membrane so that the cooled freshwater interacts with the gases of the converted ammonium bicarbonate ions and the gases reform or reassociate as ammonium bicarbonate ions that exit the draw side of the hydrophobic membrane and flow out of the draw side of the hydrophobic membrane as a concentrated ammonium bicarbonate solution. 
 
     
     
       2. The water desalination method of  claim 1 , further comprising:
 (p) directing cooler water through the draw side of the hydrophobic membrane housing; 
 (q) once the gases pass through the hydrophobic membrane of the hydrophobic membrane housing to the draw side, allowing the gases to condense into ammonium bicarbonate ions in the cooler water in the draw side of the hydrophobic membrane housing to form an ammonium bicarbonate solution, wherein the condensing occurs due to a temperature difference between the heated resulting solution flowing through the feed side of the hydrophobic membrane housing and the cooler water flowing through the draw side of the hydrophobic membrane housing; 
 (r) flowing the ammonium bicarbonate solution from the draw side of the hydrophobic membrane housing back into the inlet of the draw side of the FO membrane housing in order to desalinate a new amount of the salt water or contaminant water flowing into the inlet of the feed side of the FO membrane housing and to supply a new draw solution for the FO membrane housing. 
 
     
     
       3. The water desalination system of  claim 1 , further comprising pumping the concentrated ammonium bicarbonate solution from step (o) and redirecting the concentrated ammonium bicarbonate solution to the draw side of the FO membrane housing to be used as a new draw solution thereby reusing the new draw solution to assist in the desalination of any additional salt water or contaminant water directed through the feed side of the FO membrane housing. 
     
     
       4. The water desalination method of  claim 1 , wherein prior to step (o), flowing the concentrated ammonium bicarbonate solution to a surge tank. 
     
     
       5. The water desalination method of  claim 1 , further comprising, after flowing the resulting solution from the draw side of the FO membrane housing at step (f), flowing the resulting solution through a surge tank. 
     
     
       6. The water desalination method of  claim 1 , further comprising:
 after step (o), flowing and recirculating the first amount of the freshwater product water from the second vacuum tank to a pump one or more times before redirecting the first amount of the freshwater product water for the end use in order to pump the first amount of the freshwater product water out while maintaining the vacuum. 
 
     
     
       7. The water desalination method of  claim 1 , wherein the FO membrane of the FO membrane housing comprises a hydrophilic membrane capable of passing water through the membrane. 
     
     
       8. The water desalination method of  claim 1 , wherein the hydrophobic membrane of the hydrophobic membrane housing permits a transfer of the gases through the hydrophobic membrane and retains water on the feed side of the hydrophobic membrane. 
     
     
       9. The water desalination method of  claim 1 , further comprising, maintaining a continuous vacuum. 
     
     
       10. The water desalination method of  claim 9 , wherein the maintaining of the continuous vacuum further enables the gases to disassociate at a lower temperature than what is required if the vacuum is not maintained. 
     
     
       11. The water desalination method of  claim 1 , wherein the concentrated ammonium bicarbonate solution comprises approximately at least 25% of ammonium bicarbonate. 
     
     
       12. The water desalination method of  claim 1 , wherein the concentrated ammonium bicarbonate solution comprises between 20 to 35 percent of ammonium bicarbonate. 
     
     
       13. The water desalination method of  claim 1 , wherein the water desalination system is implemented in a water desalination plant.